Many emerging technologies, such as Internet-of-Things (IoT) and autonomous navigation, may involve detection and measurement of distance to objects in three-dimensional (3D) space. For example, automobiles that are capable of autonomous driving may require 3D detection and recognition for basic operation, as well as to meet safety requirements. 3D detection and recognition may also be needed for indoor navigation, for example, by industrial or household robots or toys.
Light based 3D measurements may be superior to radar (low angular accuracy, bulky) or ultra-sound (very low accuracy) in some instances. For example, a light-based 3D sensor system may include a detector (such as a photodiode or camera) and a light emitting device (such as a light emitting diode (LED) or laser diode) as light source, which typically emits light outside of the visible wavelength range. A vertical cavity surface emitting laser (VCSEL) is one type of light emitting device that may be used in light-based sensors for measurement of distance and velocity in 3D space. Arrays of VCSELs may allow for power scaling and can provide very short pulses at higher power density.
A Light Detection and Ranging (LIDAR) system, may determine a collection of points (e.g., a point cloud) based on reflected light. The number of points that a LIDAR system can generate per frame is one measure of the information gathering capability of the system. LIDAR systems can be flash-based or scan-based. A flash-based LIDAR application typically illuminates the entire field at once, and may use a massively parallel detector to detect points across the field and generate the resulting point cloud. A flash-based LIDAR approach can generate a large number of points at once but may have less flexibility. For example, a flash-based LIDAR application may not be able to focus on a particular target, and illuminates the entire field for every frame. Furthermore, flash-based approaches may require a focal plane array of detectors, which may impose challenges on the capabilities of each individual detector. For example, the focal plane can only be so large and therefore each individual detector can only accommodate so much circuitry and functionality.
Some scan-based LIDAR systems generate a point cloud by scanning or “sweeping” one or more narrow-field (e.g. approximately or less than 1 degree) illumination and detection regions across a target. However, scanning may require a mechanism for steering the illumination source across the field. Some LIDAR system concepts may rely on one or more of the following approaches for steering the illumination beam(s): mechanical scanning; microelectromechanical systems (MEMS)-based scanning mirrors; and coherent phased array apertures that can electrically steer a beam by selective delay of the phases in individual coherent emitters. Each of these scanning approaches may have drawbacks. The mechanical and/or MEMS-based scanning approach may suffer from reliability concerns because of, for example, moving parts. Furthermore, some MEMS-based scanning may have limitations on the range of angles that they can deliver without elaborate and complicated combinations of scanning mirrors. Phased array scanning may also face difficulties because of the extreme size and spacing tolerances that may be required in the production of individual emitter elements for operation at optical (visible and near infrared) wavelengths.